Printing systems utilizing a Raster Output Scanning (ROS) device to form images on a photoreceptor surface are well known in the art. Conventionally, the ROS includes a diode or gas laser for generating a coherent beam of radiation, a modulator for modulating the laser output in accordance with an input video image signal, and a multifaceted polygon scanner for scanning the modulated laser beam output line by line across the surface of the photoreceptor to form the latent image. Also included in the ROS are various optical components to collimate, expand, focus, and align the modulated scanning beams. These optical components are fixedly mounted within a housing frame, which is positioned within a printer machine frame, so that the modulated and shaped scanning beams emerging from a window in the housing are directed perpendicular to the photoreceptor surface to form scan lines. The lines will be formed in parallel across the surface of the photoreceptor belt. The belt should be aligned so that these parallel lines are formed perpendicular to the direction of belt travel. It is difficult to achieve this perpendicularity, resulting in a condition referred to as “scan line skew” causing a squareness error, wherein the image effectively takes the form of a parallelogram. This condition will affect the images which are subsequently developed and transferred to output prints, the output prints exhibiting degradation of quality due to the skew effects.
In the past, the ROS would be adjusted manually until the squareness error was eliminated, however, newer systems provide stepper motor driven ROS de-skew mechanisms. For example, in U.S. Pat. No. 5,374,993 an adjustment example is provided that requires a multi-step procedure of printing a test pattern, determining a registration edge skew introduced by the paper feed path, determining a lead edge skew, subtracting the registration edge skew from the lead edge skew to determine the scan line skew, loosening a clamp securing the ROS housing, determining the number of hex flat increments required to correct the scan line skew from a table, turning an adjustment screw by the indicated number of hex screw flat increments, and re-tightening the clamp securing the ROS housing.